FI102288B - Starch - based biodegradable products and method for their preparation - Google Patents

Abstract

PCT No. PCT/EP90/00375 Sec. 371 Date Nov. 5, 1990 Sec. 102(e) Date Nov. 5, 1990 PCT Filed Mar. 8, 1990 PCT Pub. No. WO90/10671 PCT Pub. Date Sep. 20, 1990.Formed articles comprising destructurized starch, an ethylene-acrylic acid copolymer and a product of the interaction of starch and ethylene-acrylic acid copolymer wherein the starch not bound to the copolymer is in the form of particles having sizes below 1 micron. The water content of such articles is lower than the one usually present in the starch. Said formed articles can also contain urea in an amount no higher than 30% by weight and/or ammonia in an amount not higher than 0.5% by weight. The process for obtaining such articles comprises the steps of extruding starch, an ethylene-acrylic acid copolymer and optionally water, urea and/or ammonia at a temperature ranging from 90 DEG to 150 DEG C., reducing the water content to values lower than 6% by weight and injection molding or extrusion blowing the resulting composition.

Description

The present invention relates to starch-based biodegradable products and thin films and to a process for their preparation.

The term "shaped articles" as used at any time in this specification and claims means all articles having a thickness of more than 0.2 mm, such as boxes, generally containers, plates, packaging materials, yarns, and the like.

In recent years, many attempts have been made to produce biodegradable products.

Among the materials proposed for the production of shaped articles and thin films, starches have undoubtedly been the most popular because they are natural, inexpensive and completely biodegradable products that are abundantly available in nature.

20 U.S. Pat. 4,591,475 describes an injection molding process using non-degradable starch as a starting material. In this case, the process was found to be very unstable due to the fact that the viscosity of the product in the molten state depended on the rate of shear deformation, therefore the compression process strongly depends on conditions such as screw speed, temperature, pressure and / or water.

In a published European patent application. 30 no. 304 401 describes an injection molding process for casings using degraded starch as a starting material. However, the products obtained by this method have poor mechanical properties, in addition to being highly water-soluble.

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It has also been proposed to combine starch with other materials to obtain products with satisfactory characteristics. Polyethylene is the material commonly proposed for this purpose. However, various attempts to make shaped articles using starch-polyethylene blends as starting materials have not yielded satisfactory results. In fact, the products are shapeless and weak because they have a lot of pores as the moisture 10 turns to steam during the molding process. In addition, the products obtained have a tactile feel like paper.

U.S. Patent No. 4,133,784 describes compositions containing starch and ethylene-acrylic acid copolymer (EAA) that are suitable for conversion into thin films and that are flexible, water resistant, heat sealable, and biodegradable.

Said compositions are converted into thin films using methods such as casting, simple extrusion or grinding. However, these processes are 20 slow and very expensive. In addition, at certain starch concentrations necessary to achieve the desired mechanical properties, the degree of biodegradation and stability to ultraviolet rays are severely degraded.

25 On the other hand, many of the applicant's attempts to mold these compositions by spraying were unsuccessful because of the poor physico-mechanical properties of the products obtained; in fact, the products had low strength and high elongation under load.

. U.S. Patent No. 4,337,181 proposes adding a sufficient amount of a neutralizing agent, such as ammonia or amine, to the starch-> EEA copolymer composition to neutralize some or all of the EEA acid groups, and then blow molding using a moisture content of 2-10%.

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The addition of a neutralizing agent makes it possible to overcome some of the difficulties associated with the film-forming process, while the disadvantages which depend on the low strength of the products obtained remain the same or increase.

In Ind. Eng. Chem. Res. 1987, 26, pp. 1659-1663, it was proposed to add urea and / or polyols to starch-EAA copolymer compositions to facilitate preparation and to improve the economy and quality characteristics of the resulting thin film. The effect of the presence of urea is to allow the crystal structure of the starch to break down with small amounts of water, thus allowing film-forming granules to form directly from a composition with a water content of about 16%, and eliminating the need to form a starch-15 EEA copolymer premix in a very complex mixer. before the extrusion process. Therefore, the addition of urea improves the process conditions of the starch-EEA copolymer blend, while the poor physico-mechanical properties of the obtained products remain.

The applicant has now found that shaped articles produced by injection molding technology and thin films produced by extrusion blow molding have excellent physico-mechanical properties. Such as fracture toughness, high flexural strength and coefficient, which are much higher than the values of the individual components, as well as insolubility in water, when said bodies and thin films contain the following three components completely penetrated: 30 (1) component consisting of decomposed , starch in particulate form with a number average particle diameter of less than 1 μιη, (2) a component consisting of ethylene-acrylic acid copolymer (EAA), 4 102288 (3) a component consisting of an IPN structure consisting of obtained from the interaction of starch and ethylene-acrylic acid copolymer by mixing starch and ethylene-acrylic acid copolymer in a weight ratio of 1: 9 to 9: 1 in an extruder heated to 90-150 ° C until the starch has substantially decomposed and the substances have infiltrated () water less than 6% by weight of the total weight of said three phases.

10 The product from the interaction of starch and EAA copolymer is obtained in situ during the conversion process of the starting materials into a shaped body.

Preferably, the ethylene-acrylic acid copolymer (EAA) has an acrylic acid content of 3 to 30% by weight, and the decomposed starch phase not bound to the EEA copolymer is uniformly dispersed in the mixture as particles having a number average diameter of less than 1 μπι. particle size less than 3, as a dispersion.

The dispersion of the dispersed starch particles is defined as the ratio between the number average diameter and the average surface diameter.

The ratio of the various components of the composition may vary depending on the properties obtained, the temperature and the shaping process. Usually shaped bodies and thin films with excellent physico-mechanical properties and insolubility in water contain: - 10 to 90% by weight of the total amount of degraded starch; - 10 to 90% by weight of the total amount of EAA copolymer having an acrylic acid content of 3 to 30% by weight; and '· - 0 to 6% water, wherein less than 40% by weight and preferably less than 20% by weight of the total starch is free and in particles with a number average diameter of less than 1 μτη, while the remaining 35 starch is bound to the EAA copolymer forming an IPN product.

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The shaped bodies and thin films which are the subject of this invention may also contain urea added to the starting material mixture to improve its processability. If urea is present, its amount does not exceed 30% to 5% by weight and preferably 5 to 20% by weight of the mixture.

The water content of the bodies of this invention is usually less than the amount of water normally present in the starch. Usually the water content does not exceed 6% by weight, and the water may also be completely absent.

Ammonia, optionally added to the starting material mixture to improve the preparation of the composition, is removed either during the extrusion process or after the drying step, so that the products of this invention do not contain ammonia or the ammonia content does not exceed 0.5% by weight of the mixture.

The process for making shaped articles and thin films, which is another object of the present invention, consists of a mixture of starch and EEA copolymer in a starch / EEA copolymer weight ratio of 1: 9 to 9: 1, water and optionally urea and ammonia, mixing the components in an extruder heated to 90-150 ° C, changing the water content to less than 6% by weight and changing the ammonia content to less than 0.5% by weight.

Reducing the water content prior to further processing of the composition is an important feature of the method of the invention.

. The reduction of the water content and possibly the ammonia content can be carried out either by direct ventilation in an extruder or by drying at a temperature of about 70 to 100 ° C in an air stream or under reduced pressure after the extrusion step.

In accordance with the preferred method 6 102288 for producing the shaped bodies and thin films of the present invention, the reduction of the water content is performed in an intermediate degassing step of the extrusion process.

Accordingly, this method involves feeding material 5 to an extruder heated to 90 to 150 ° C, wherein the material is starch and an ethylene-acetic acid copolymer having a starch / copolymer ratio of 1: 9 to 9: 1, and water , in an amount of 10 to 25% by weight of the starch component, and treating the fed material 10 as follows: - a first step in which the fed starch is effectively mixed with the copolymer until it is substantially decomposed and the substances have passed through each other, the material is degassed to reduce its water content to not more than 2% by weight of the composition, and - a step of transferring and compressing the degassed material at a pressure of more than 500 Pa and extruding the material at a temperature of 105 to 130 ° C.

After the first mixing step, the fed material is preferably subjected to a transport step, during which the temperature of the material continuously rises to 60-100 ° C. The length of the transport zone of the extruder is typically between 4 and 20 times the diameter of the extruder screw.

The next mixing step is preferably carried out at a temperature between 105 and 140 ° C under conditions such that the starch at the same time substantially decomposes and penetrates the copolymer. The mixing zone is preferably ·· 4-20 times the length of the screw of the extruder, and the material is subjected to a shear deformation at a speed of 50 to 5000 S1.

The phenomena which occur at this stage and which lead to the decomposition of starch are known and are usually explained by the formation of a disorder in the molecular structure of the starch particles as a result of heat treatment above the glass transition temperature and melting points of its components.

The degassing step may typically include 1 to 4 degassing zones in which a pressure below atmospheric pressure is applied to the body of the extruder, usually 690 to 700 mm Hg. At this stage, the amount of water can fall to values of 2 to 0.1%, preferably less than 1%. Degassing is performed using one or more water ring pumps of a known type.

The degassed material then goes through the next transport step with only transport elements or mixing elements and then transport elements to improve penetration and prevent the mixture from losing the uniformity formed during the first mixing step. The length of the conveying zone is usually 4 to 20 times the diameter of the extruder screw.

The molten material is then compressed to a pressure of more than 500 Pa, preferably more than 1500 Pa and more preferably more than 3000 Pa using compression ratios of 1: 1.5 to 1: 4. The extruded material is then extruded into wires or sheets, preferably at a temperature between 105 and 130 ° C.

1 25 Extruded sheet can be used for thermoforming using either vacuum technology or male / female molding method. The granules or pieces can be made of extruded yarn or film, respectively, and can then be used for film blowing, preferably at a temperature of: between 100 and 140 ° C by conventional methods, or can be used for injection molding.

In particular, it has been found that in order to reduce the water content to less than 2% by weight and more preferably to less than 1% by weight, a degassing step between two mixing and transfer-compression steps carried out under conditions such that the starch decomposes and enters an infiltrated structure provides a particularly suitable extrudate. well to the next step of the process by extrusion and compression.

5 The film blowing bubble is perfectly flat and the ducts do not have tack problems. In addition, the modulus of the thin films is increased and they are able to withstand deformations and stresses greater than or equal to those tolerated by the thin films described in U.S. Patent Application No. 10,413,784 and U.S. Patent No. 4,227,181.

Molded bodies are obtained by injection molding the composition obtained at a temperature of 130 to 180 ° C, preferably 130 to 160 ° C, with a shear deformation rate of 15 to 10,000 s'1 over a period of 10 to 120 s, preferably 3 to 60 s, depending on the desired body. thickness.

The molding temperature and shear rate, in addition to the ammonia and water content of the composition, are critical parameters of the process of this invention to obtain molded articles having the required typical properties.

In fact, it was found that if working under such conditions, it is possible to obtain disintegrated starch particles which are uniformly distributed in the matrix and have a number average diameter of less than 1 μιη, preferably 0.1 to 0.5 μπι, and a particle size dispersion of less than 3, and to form an in situ interaction product between the starch and the EEA copolymer in a ratio such that it binds at least 60% and preferably 80; 30 to 100% of the starch used as starting material.

The shaped articles of this invention have good physico-mechanical properties such as a modulus of more than 500 kg / cm 2, good tensile strength; they have a high flexural strength of the order of 300 to 400 kg / cm2 and are insoluble in water. Such bodies suffer from a deterioration in their physical-mechanical properties when immersed in water, but their shape remains unchanged and no changes occur on their surface; by aeration them in 5 atmospheres at 25 ° C and 50% relative humidity, such bodies tend to become translucent and more brittle.

The term "starch", as used in this specification and claims, generally means all starches of natural or vegetable origin, consisting essentially of amylose and / or Amy-lopectin. They can be extracted from various plants such as potatoes, rice, tapioca, corn and cereals such as rye, oats, wheat, etc. Maize starch is preferred. The term "starch" also refers to starch modified to lower the acid number in the range of 3-6, as well as potato starch in which the type and concentration of cations attached to the phosphate group have been modified. Ethoxylated starches, acetate starches, cationic starches, oxidized starches, crosslinked starches, etc. can also be used in the process of this invention.

Starch of natural origin can be used as such without prior drying at a natural bound water content of the order of 10 to 13% by weight. An amount of water that gives a total water content of no more than about 25% of the total weight of the dry starch, preferably 10-15%, is added to the starch in the extruder.

; The EAA copolymer used in the process must contain a sufficient number of carboxyl groups to be compatible with the starch. The presence of carboxyl groups also makes the copolymer dispersible in water. The preferred EAA copolymer is one obtained by copolymerizing a mixture containing 3 to 30% by weight, preferably 20 to 102288% by weight of acrylic acid and 97 to 70% by weight, preferably 20% by weight of acrylic acid and 97% by weight, respectively. -70% by weight, preferably 80% by weight of ethylene. The starch / -EAA copolymer ratio is preferably between 1: 4 and 4: 1.

Naturally, an increase in the starch content towards higher values in the above range is advantageous for the biodegradability of the films produced.

The addition of urea to the material fed to the extruder has been found to be advantageous in facilitating the decomposition of the starch and making it compatible with the EAA copolymer. If urea is present, its amount is not more than 30% by weight and preferably between 5 and 20% by weight of the total composition.

Ammonia may optionally be added to the starch-EAA copolymer in a non-critical amount, usually up to 7% by weight (30% saturated ammonia solution) of the weight of the dry starch. The added ammonia is then completely or partially removed during the extrusion of the composition or during the drying step or during the intermediate degassing.

In fact, the final products are known to be substantially free of ammonia, which in any case remains in very small concentrations, always less than 0.5% by weight, preferably less than 0.2%.

Polyethylene can also be added to the composition to improve the resistance of the final product made from it to ultraviolet radiation.

30 Any type of polyethylene can be added, *: although LD polyethylene is the one commonly used for this purpose. The amount of polyethylene added is usually less than 40% by weight of the mixture.

Other materials, either polymeric or monomeric, may be added to the composition prior to the extrusion step. Thus, for example, various amounts of polyvinyl alcohol may be added to convert the shaped bodies from water treatment; UV stabilizers such as carbon black can be added to improve the resistance of the bodies to sunlight; refractory materials may be added in such a case that, when shaped, the bodies must have said property. Other additives include the usual additives commonly added to starch-based moldable compositions, such as fungicides, herbicides, antioxidants, fertilizers, opacifiers, stabilizers, plasticizers, etc. All of these additives can be used in ordinary amounts known to those skilled in the art. or which can be easily determined by ordinary experiments 15 and may amount to up to 20% by weight of the final composition.

The following example is provided to illustrate the present invention.

In the example, all percentages are by weight unless otherwise indicated.

Example 1

A composition was prepared containing the following components: 37% by weight of starch Globe 3401 Cerestar with a water content of 11% to 37% by weight of EEA copolymer 5981, manufactured by Dow Chemical, containing 20% of acrylic acid; - 6.8% by weight NH 4 OH, 30%; - 6.8% by weight of water; and 30 to 12.4% by weight of urea.

The products were premixed and then fed to a Baker Perkins MPC / V-30 extruder using a Licoarbo DC-10 dispenser. Such an extruder consisted of a twin-screw combination divided into two parts. The diameter of the screw-35 was 30 mm and the length-to-diameter ratio of the screw • 102288 12 (L / D) was 10: 1; the combination was connected to a single-screw extruder with a capillary head and a 38 mm diameter screw with an L / D ratio of 8: 1, divided into three parts. The diameter of the capillary head 5 used was 4.5 mm.

The temperatures used were 80 ° C in the two parts of the twin-screw combination and 120 °, 100 ° and 130 ° C in the three parts of the single-screw extruder, respectively.

The driving conditions were as follows: 10 - twin screw extruder speed: 250 rpm - single screw extruder speed: 110 rpm - chamber pressure: <40 atm.

The extruded product was cooled in air and then granulated with an OMC granulator. The resulting mixture was dried at 100 ° C under reduced pressure for 4 hours before injection molding. The water content of the mixture after drying was 0.3% by weight and the ammonia content was less than 0.1% by weight.

The dried mixture was injection molded using a SANDRET-TO press 57/60 with two capillary tubes placed symmetrically at the bottom of the body to be molded.

25 The driving conditions were as follows:.

- injection temperature: 155 °, 165 °, 180 ° C

- mold temperature: 25 ° C

- shear rate (s-1): 2000-6000 s'1 - total injection time: 15 s -.30 - total cycle time: 45 s: - holding pressure: 400 bar The samples thus obtained had a box-shaped shape and were geometric truncated pyramids with a geometric structure the smaller base had a size of 13 102288 60 x 60 mm and the larger base 67 x 67 mm, height 60 mm and thickness 3 mm.

The elemental composition of the obtained samples was as follows: C = 56.70% 5 H = 9.55% N = 6.6% The presence of ammonium salts was not observed in the IR spectrum, so it showed the absence of ammonia.

The sizes of the decomposed starch particles unbound in the EAA copolymer were measured by analysis by transmission electron microscopy (Philips EM 300) of a small chip of the product obtained with an ultramicrotome (Nova LKB).

The number average diameter and the average 15 'surface diameter were obtained using particle sizes obtained from micrographs at 6000 and 10,000x magnification taken from different points in the sample.

In the obtained product, the number average diameter of unbound starch particles was 0.44 μπι. The ratio of the mean surface diameter to the number average diameter was taken as a measure of particle dispersion. In the product obtained, said ratio was 1.44.

The bending properties measured according to ASTM D 790 were as follows: - Young's modulus: 7000 kg / cm2 - yield point: 310 kg / cm2 - elongation: 11% The sample was left in water at 30 to 20 ° C for 20 days and then allowed to air for one month at room temperature and humidity of about 50%.

The centesimal analysis of the conditioned sample was as follows:

C = 57.75M

35 H = 9.8% N = 2.45%.

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The number average diameter of the unbound starch particles was 0.36 μπι and the dispersion of the particles was 1.58.

Bending properties measured according to ASTM D 790 standards were as follows: - Young's modulus: 5000 kg / cm2 - yield strength: 230 kg / cm2 - elongation: 13%

Example 2 The following composition was fed to a twin screw extruder with a screw diameter of 50 mm and a screw length / diameter ratio of 36: 4.0 kg of starch GLOBE 03401 Cerestar, which had not been pre-dried, 1.2 kg of urea, 4.0 kg of Dow Chemical1 copolymer EAA 5981 with an acrylic acid content of 20%, 0.6 liters of water.

The extruder had the following zones: 20 transport zone: 4 diameters, first mixing zone: 20 diameters, degassing zone connected to a vacuum at a pressure of about 690 mm Hg, transport zone with mixing elements: 11 diameters, 1 compression zone, compression zone The set temperatures were in the transport zone 60 and 80 ° C and in the following zones 90 to 130 ° C. The experiments were performed using screw speeds of 100 and 250 rpm and a head pressure of 40 atm (4000 Pa).

-: The molten material was extruded using an outlet temperature of 120 ° C and a water content of about 0.7%.

The wire-like extrudate was pelletized and the pellets were fed into a HAAKE extruder having a diameter of 19 mm 35 and a ratio L / D 25 and a film blowing head. The extrusion and blowing process was performed using screw rotation speeds of 30 to 65 rpm and a compression ratio of 1: 2.

For tensile tests according to ASTM 882, rectangular test pieces with a delta thickness of about 100 μττι were taken from the films 5.

The test pieces were conditioned at 23 ± 1 ° C and 55 ± 5% relative humidity for 24 hours.

The following results, expressed as averages, were obtained from the mechanical strength tests.

Young's modulus 200 kg / cm2

Elongation at break 150%

Tensile strength 150 kg / cm2

In all experiments, the tubes obtained by blowing 15 had no tack problems and the bubble was smooth and stable.

Similar results were obtained when a composition as described above, which additionally contained 6.0 liters of a 30% ammonia solution, was added to a twin-screw extruder.

20 Example 3

Pellets prepared as in Example 2 were fed to an extruder with a diameter of 35 mm and an L / D 20 ratio, with a flat end plate and internal water cooling (cirrol) in the cylinder.

The process for producing a thin film was carried out at a screw rotation speed of 40 rpm and a temperature of 110 to 130 ° C and a compression ratio of 1: 2.

The water cooling temperature was about 15 ° C.

Thus, it was possible to produce films having a thickness of 20 to 299 μχη by varying the output rate. The stretching properties of the thin film tested according to ASTM standard 882 were: 102288 16

Extrusion direction of extrusion direction_

Young's modulus 2200 kg / cm2 1500 kg / cm2

Elongation at break 200% 120% 5 Tensile strength 140 kg / cm2 115 kg / cm2

Example 4

The pellets prepared according to Example 1 were fed into an extruder with a diameter of 50 mm, a L / D ratio of 20, a flat end plate about 70 cm wide.

This type of flat end plate for PP and PE had a torsion bar which ensured that the outlet velocity of the molten material was constant at each point.

The extrusion conditions for a film with a thickness of 0.8 mm were as follows: - temperature 140 eC through the extruder, 20 - screw rotation speed: 60 rpm, - end plate opening: 1 mm.

The film was assembled on a calendar with a rack of three water-cooled rollers.

The film thus obtained was formed into a male / female plate account measuring 20 cm x 15 cm after the film was heated to 80 ° C.

The plate thus obtained was uniform in thickness.

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Claims (18)

1. Water-insoluble products based on starch, characterized in that they comprise a 5 (1) component consisting of dispersed starch in particulate form with a number average particle diameter of less than 1 μιη, (2) a component consisting of ethylene-based starch. acrylic acid copolymer (EAA), a 10 (3) component consisting of an IPN structure obtained from the interaction of starch and ethylene-acrylic acid copolymer by mixing starch and an ethylene-acrylic acid 9 copolymer in an extruder heated to 90-150 ° C 1 until the starch has substantially disintegrated and the substances have penetrated each other, and optionally (4) water which is less than 6% by weight of the total weight of said three phases. Starch-based products according to Claim 1, characterized in that their ethylene-acrylic acid copolymer has an acrylic acid content of 3 to 30% by weight and the decomposed starch phase which is not bound to the ethylene-acrylic acid copolymer is finely divided and evenly distributed. as particles * 25 with a number average diameter of less than 1 μτα and a particle dispersion of less than 3. Starch-based products according to Claim 1, characterized in that they contain: 30 to 10 to 90% by weight of the total amount of ethylene-acrylic acid copolymer having an acrylic acid content of 3 to 30% by weight, and - less than 2% by weight. water; wherein less than 40% by weight and preferably less than 20% by weight of the total starch is free and in the form of particles having a number average diameter of less than 1 μπι, and the remaining starch is bound to the ethylene-acrylic acid copolymer to form said interaction product. Starch-based products according to Claim 3 to 5, characterized in that 80 to 100% of the total starch is bound to the ethylene-acrylic acid copolymer. Starch-based bodies according to Claim 2 or 3, characterized in that the particles have a number-average diameter of 0.1 to 0.5 μπι. Starch-based products according to Claim 1, characterized in that the ethylene-acrylic acid copolymer has an acrylic acid content of 20% by weight. Starch-based products according to one of the preceding claims 1 to 6, characterized in that the water content is 0 to 2% by weight of the mixture. Starch-based products according to Claim 1, characterized in that they additionally contain at most 30% by weight of urea from the mixture or at most 0.5% by weight of ammonia from the mixture. Process for the preparation of starch-based products, characterized in that - starch and ethylene-acrylic acid copolymer in a weight ratio of 1: 9 to 9: 1, water 10 to 25% of the total weight of the starch component are fed to an extruder heated to 90 to 150 ° C and optionally urea and / or ammonia, - in the first mixing step, the starch is thoroughly mixed with the copolymer until it is substantially decomposed and the substances have penetrated, - the material obtained from the mixing step is degassed and the water content is less than 6% by weight, preferably less than 2% by weight, and an ammonia content, if less ammonia, of less than 0.5% by weight, and 19 102288 - the material obtained is further transferred and pressed to a pressure of more than 500 Pa and the material is extruded at a temperature of 105 to 130 ° C. A method according to claim 9, characterized in that the first transport step at a temperature of 60 to 100 ° C is immediately after the first mixing step. A method according to claim 9, characterized in that the material fed to the extruder is subjected to a shear deformation at a speed of 50 to 5000 s'1 during the first and second mixing steps. A method according to claim 9, characterized in that the first mixing step is 4 to 20 times the length of the screw of the extruder. A method according to claim 9, characterized in that the step of conveying the degassed material is 4 to 20 times the length of the screw of the extruder and includes mixing elements which can prevent the separation phenomenon. Method according to Claim 9, characterized in that a compression ratio of 1: 1.5 to 1: 4 is used in the compression step. Process according to Claim 9, characterized in that the material fed to the extruder contains at most 7% of ammonia by weight of the dry starch and in which the ammonia content is reduced to at most 0.2% by weight of the weight of the extruded composition in the degassing step. Process according to Claim 9, characterized in that the material fed to the extruder contains at most 30% by weight of urea, preferably from 5 to 20% by weight of the total weight of the composition and from 10 to 15% by weight of water of the dry starch component. 102288 20 Process according to Claim 9, characterized in that the starch and the copolymer are fed to the extruder in a ratio of 1: 4 to 4: 1. 17 102288 A method of making molded articles according to claim 9, characterized in that the extruded composition having a water content of less than 6% by weight is injection molded at a temperature of 130 to 180 ° C at shear deformation rates of 1000 to 10,000 s'1 for 10 to 120 seconds. depending on the thickness. 21 102288